U.S. Pat. No. 3,570,569 discloses a food mixing machine provided with a grinder which is designed so that the mixer can be operated either independently of or in conjunction with the grinder. Machines of this type are used extensively for preparing food products, particularly meat. The products deposited in the hopper of the mixer-grinder machine may include, in addition to seasonings and other additives, both frozen and unfrozen meat.
The frozen meat may be in stick form, which results from sawing blocks of frozen meat into elongated sticks, but a more popular form is in the form of chips or flakes which result from dividing the meat with a rotating blade device similar to a wood planer. Although chips tend to feed faster and therefore jam in a grinder they are more popular since their preparation requires less labor. While all of the meat products deposited in the hopper may be in frozen chip or flake form, more common practice is to have only a portion of the hopper contents frozen with the remainder unfrozen.
In either case, if the frozen particles are fed into the grinder barrel too rapidly by the feeder worm an excessively large worm driving torque is required since frozen particles are not readily extruded from the barrel through the grinder plate in the same manner as unfrozen meat, but must in reality be heated to at least a semi-plastic state (near 26 .degree. Fahrenheit, for example) before passing through the grinder plate. It is therefore found that the pressure of a large quantity of chips in the barrel may cause the machine to stall.
One possible solution to this problem would be to control carefully the amount of frozen particles deposited in a grinder hopper. In practice, however, this is impractical since it requires constant monitoring of the feed operation and since the feeder worm is found to have an affinity for chips, particularly chips of a certain size. Another approach is to increase the capacity of the motor and gear train of the machine. Obviously, this solution appreciably increases the cost and energy supply requirements of the machine.
Many prior art patents are directed to the feeding of products into mixers and/or grinders, such as U.S. Pat. No. 3,213,911. In this patent, a separate shaft is provided having radially projecting arms or blades with sharp cutting edges mounted thereon adapted to rotate between the turns of the conveyor screw. It will be apparent, however, that this provision requires additional bearings and drive for the shaft carrying the cutting blades, and would both increase the cost of the machine and require additional cleaning time.
Other patents of interest in this area are U.S. Pat. Nos. 309,381; 443,590; 474,595; 1,056,153; 1,736,333; and 2,210,006. In each of these patents, as in U.S. Pat. No. 3,213,911, an attempt is made to comminute pieces of material and a common approach, as shown in some of these patents, is to utilize cooperating moving and stationary blades for this purpose.
Also of interest with regard to improvements in material feeder worms is U.S. Pat. No. 2,072,406 wherein a material dispersing projection is added near one end of the coal feeding worm of a steam locomotive. In this patent the worm projection is added for the purpose of dispersing coal which would otherwise accumulate and cause a jam when the worm is reverse driven during the dislodging of an obstructing object.